Cut the spring onions into small pieces.
Put the vinegar and water in a saucepan and add all ingredients, except the spring onions.
Bring to the boil, while stirring. When boiled, add the spring onions and turn off the heat.
Put a lid on and rest for 5 minutes, then transfer the pickled onion to a sterilised jar, adding enough liquid to cover the pieces fully.
Seal the jar and let it cool, then keep it in a cold larder - after opening, in the fridge.
Use any remaining liquid as salad or relish dressing.